The present invention generally relates to the field of frequency division, such as used for signals in the GHz range, and more specifically, to an apparatus and method for a dynamic frequency division by four.
For various applications in electronics, there is a need for frequency dividers at very high frequencies up to several 10 GHz. Furthermore, frequency dividers are used in a wide variety of important high-speed and radio-frequency (RF) integrated circuits, such as in phase-locked loops (PLLs) and other telecommunication devices. However, conventional static frequency dividers are not suitable for high operating frequencies and instead so called dynamic frequency dividers are employed for this purpose.
Originally proposed by Miller in 1939, the dynamic frequency divider is based on mixing the output signal of the mixer with the input signal and applying the result to a low-pass filter (LPF), as illustrated in FIG. 1. Under proper phase and gain conditions, the component at ωin/2 “survives” and circulates around a loop. Since the device capacitances are absorbed in the low pass filter, this topology achieves a high speed.
The example illustrated in FIG. 1 illustrates that an input signal X(t) with a frequency ω is mixed by a mixer 1 to the two sideband frequencies ωin/2 and ωin 3/2. The frequency ωin3/2 is then filtered out by a low-pass filter 2 leaving only the signal with ωin/2 to be looped back to the mixer eventually producing an output signal y(t), which is the input signal X(t) divided by two.
Mixers used for frequency conversion are critical components in dynamic frequency division. A mixer converts, for example, RF signals of one frequency into signals of another frequency to make signal processing easier and also inexpensive. Another fundamental reason for frequency conversion is to enable amplification of the received signal at a frequency other than, for example, the RF or audio frequency.
An ideal mixer is a device that multiplies two signals producing an output signal with a new frequency spectrum. Hence, the mixer essentially shifts the frequency spectrum of the input signal using a signal of higher or lower frequency into a new signal with two frequency components that are the sum and difference of the two signals frequencies.
An operation converting a high frequency signal into a low frequency signal is called down conversion and an operation converting a low frequency signal into a high frequency signal is called up conversion.
A regenerative frequency divider by N (N≧2), based on special loop-filter, was proposed by Miller in R. L. Miller, “Fractional frequency generators utilizing regenerative modulation” Proc. I.R.E., pp 446-457, 1939, although, the regenerative dividers subsequently designed and studied have been exclusively divide-by-two configurations.
Frequency dividers with greater division ratios have been described, for example, in J. F. Garcia Nava, A. Hati, C. W. Nelson, A. Sen Gupta, F. L. Walls and T. N. Tasset, “Parallel configuration for conjugate regenerative dividers”, IEEE Int. Freq. Control Symposium and PDA Exhibition, 2003, A. S. Gupta, J. F. Garcia Nava and F. L. Walls, “A noval low noise regenerative divide-by-four circuit”, IEEE Int. Freq. Control Symposium and PDA Exhibition, 2002, and A. S. Gupta, F. F. Garcia Nava, and F. L. Walls, “Conjugate regenerative dividers”, IEEE Trans. on Ultrasonic, Ferroelectric, and Frequency control, Vol. 51, No. 3, March 2004.
However, in order to obtain frequency divisions higher than two, frequency dividers have to be either cascaded or complicated filter systems have to be included into the transfer function of the feedback loop. Also, the power consumption is relatively high and the circuitry utilizes a considerable amount of space due to the increased number of electric components needed, making conventional dynamic frequency dividers complex and expensive.
A regenerative divider with a division raisure of N, where N is greater than two, based on multiple mixing of an input signal with a sample of the output signal is described in U.S. Pat. No. 3,605,023. The divider described therein incorporates two mixers, as well as low-pass filter means within the mixters.
U.S. Pat. No. 6,144,846 describes an example of a double-mixer, within a frequency translation circuit translating an incoming reference signal to a lower frequency.